The processing of meat, poultry, fish, and other food products has traditionally been a labor-intensive endeavor. In an effort to streamline operations while increasing output, many food processors have turned to automated systems for cutting and packaging their products. These systems, ranging from the simple to the very complex, have gained widespread acceptance in the industry and have started to rival their human counterparts in accuracy, while exceeding them in speed.
One of the automated systems developed for food processors was a system for generating a mapping of the mass of a product. Knowing how the mass was distributed in a product allowed a processor to cut the product into portions of specified weight. To determine the mass map of a product, an indirect estimate of the mass was usually made based on the volume of the product. In a typical method, a curtain of light was directed towards the top surface of a product as it was carried on a conveyor belt. The curtain of light appeared as a bright stripe of light on the material. Video cameras would monitor the deflection of the light stripe, and a computer would process the information from the video cameras to determine the height of the product above the conveyor belt. The system would store the height measurements to form a profile map of the material as it was carried through the light curtain on the conveyor. Once a profile map was generated, a computer would divide the product into a series of volume elements that extended from the surface of the product down to the conveyor belt. The mass of each volume element was calculated by multiplying the volume of each element by a pre-set density of the material. Adding the mass values of all of the volume elements gave the total mass of the product.
While the light curtain method succeeded in approximating the mass of a product, the method suffered from several inherent problems. Most problematic was that variations in the density within the material, or the existence of air pockets under the material, resulted in inaccuracies in the mass measurement. Only if the product were of uniform density and flush with the surface of the conveyor would the mass be exact. Further, the use of a light curtain to determine the height of the product also produced problems as the light stripe was often hidden behind undulations in the surface of the material or indistinct due to the color of the material being weighed. What was required to resolve these problems was a system that would directly measure the mass of the product.
Some of the more recent automated food processing systems have started to use x-rays to directly inspect and image food products. X-rays are attenuated as they pass through matter in proportion to the total mass of the materials through which they pass. The intensity of an x-ray received at an x-ray detector after it has passed through an object is therefore inversely proportional to the density of the object. For example, x-rays passing through a chicken bone, which has a relatively higher density, will be more attenuated than x-rays that pass through the meat of the chicken, which has a relatively lower density. Manufacturers of food processing systems have realized that the characteristic attenuation of x-rays may be advantageously used to examine and inspect food products.
Prior an systems that use an x-ray source to inspect or image food products generally fall within two categories. At one end of the spectrum are very simple systems that use x-rays to detect food products that contain defects such as unwanted bones or foreign matter. In these simple systems, x-rays are directed through food products, such as poultry, beef, or fish, toward an x-ray detector. By appropriately processing the signal from the detector, a computer can determine if the food product passing over the detector contains an unwanted bone or other foreign object. Items that contain unwanted material are separated for further processing or for disposal. In this manner, products of an acceptable quality can be quickly and easily sorted from defective food products. At the other end of the spectrum are extremely complex automated butchering systems such as that described in U.S. Pat. No. 5,162,016 to Malloy. Malloy discloses a system wherein an entire carcass of an animal is 3-dimensionally imaged using x-rays and then automatically segmented into primals under computer control. A carcass is positioned on a mounting vehicle before entering an imaging station. At the imaging station, two television cameras examine the exterior of the carcass, and a pair of orthogonally-mounted x-ray scanners map the interior of the carcass. By scanning with high and low energy x-rays, the x-ray scanners can identify and produce a three-dimensional image of the carcass's meat, bones, and muscles. After the carcass has been fully scanned, the mounting vehicle moves the carcass to a cutting station. There, under computer control, high pressure water jets cut the carcass based upon the scanned internal and external configuration; the computer guiding the cutting jets around bone or fat. The pieces removed from the carcass are then carried away on a conveyor belt for further processing.
While the two systems discussed above are certainly beneficial to the food processing industry, their use is rather specialized. The simple system can detect defects within meat, but is only used to reject bad products. In contrast, Malloy's system can accurately detect the location and orientation of any defects or structures within the carcass, including bones, muscles, abscesses, or foreign objects. The information can then used to guide cutting devices to remove the meat from the unwanted material. Unfortunately, this complexity comes at a price. The system is large, expensive, and has relatively slow throughput, greatly limiting its application.
What neither of the systems suggest is a third use of x-rays that is significantly different than sorting or complex imaging of food products. Specifically, x-rays can be used as a quick and inexpensive method of weighing food products. This previously unrecognized use of x-rays will allow producers of food products to automatically and accurately determine the weight of products before labeling or portioning.